Cable television systems, or Community Access Television (CATV) systems, generally comprise a source of cable information (program), a headend, with such systems typically including a satellite receiving device, such as a satellite dish, and a network of cables connected between a cable facility and customers of the cable provider. These systems typically operate in the 50 MHz to 1 GHz spectrum for transmitting signals downstream from the cable source to the end consumer.
The network of cables typically is provided adjacent to other utilities, such as telephone lines and electrical power cables. The network of cables reach homes and businesses from an overhead connection or through underground connections, depending on the means that the electrical and telephone service is provided in the area. In both situations, the cable access to a particular residence or business is provided via a local tap through a cable directed to the destination location, which cable is attached to a ground block and is then routed into the destination location. It is now a practice to also provide high-speed data communications via cable systems. The telecommunications industry has rapidly upgraded coaxial cable systems to facilitate bi-directional communications services. Bi-directional communications services include Plain Old Telephone Service (“POTS”), Internet access, high speed data exchange, interactive video, and other services. Upstream signals from the residence to the cable facility are typically transmitted in the 5 to 50 MHz spectrum. This facilitates two way communications. The upstream path is used with devices such as cable modems and special services devices, such as burglar alarms, fire alarms, and personal health monitors.
While downstream CATV signals are typically of very high quality, upstream signals are more susceptible to noise and interference. Typically, downstream CATV signals are superior to upstream signals because each subscriber receives CATV signals from an individual tap connected directly from the cable system. On the upstream side, however, signal interference accumulates from each subscriber as the signals return towards the cable source.
Because the upstream signals are all typically in the same frequency range, they are particularly susceptible to radio frequency (RF) energy ingress signals from everyday electrical devices. RF signals or ingress enter coaxial cables through weak points or leaks in the system and generally travel upstream. Such signals enter the coaxial network and combine with RF ingress from other points in the network on a power basis as the signals make their way through the network to the headend. The accumulation of errant ingress signals in the 5 to 50 MHz region can render a bi-directional system useless. It is, therefore, necessary to have an ingress integrity system that can detect the RF ingress and the location of RF ingress into the system.
In a typical cable system, the upstream path uses digital signals which are susceptible to unreliable operation if interference signals are present. Examples of devices capable of causing interference are: CB radios, hair dryers, washing machines, food mixers, toasters, vacuum cleaners, and almost any home appliance that has a motor or a power switch. The interference may last for an instant or may be continuous while the device is on, but in either event can catastrophically effect the communication desired.
Ingress problems in the upstream path are typically compounded by the multitude of residences connected to the CATV distribution system. Any one residence is capable of adding an interference signal to the upstream path and degrading and/or inhibiting communications. A multitude of residences, each only adding only a small amount of interference, can also render the upstream path useless because interference signals add on a power basis.
Further, the CATV cabling inside a residence is typically hidden in areas such as crawl spaces, behind walls, attics, and basements. The effects of aging on the cable (especially metal connectors), damage caused by rodents, and possibly improper installation may reduce the shielding integrity of the system within the residence. Poor shielding integrity permits the inside cabling to essentially become a “receiving antenna” for interfering signals. A signal or noise entering (ingress) the internal cabling may travel upstream and cause problems.
Currently, RF detection is accomplished by maintenance personnel in a vehicle driving around the cable plant (network of cables) with transmitters. The transmitters radiate a specific RF signal which can be identified when it leaks into the cable system. This approach is clumsy and unable to provide correlation between the ingress and the location of the mobile transmitter that is providing the test.
U.S. Pat. No. 5,777,662, (the '662 patent), assigned to the owner of the subject invention, Comsonics Corporation of Harrisburg, Va., discloses a system for radiating a signal for capture by cable systems having ingress and egress problems. The system of the '662 patent utilizes a signature RF signal with a GPS (Global Positioning Satellite) signal encoded therein, thus allowing the upstream cable distribution system to determine if an ingress is occurring and, by analysis of the GPS data, the location of the ingress. It is believed that more precise GPS signals would provide more accurate determination of the house or business that is the source of the ingress. However, without a more precise GPS signal, it is still necessary to determine the source of the signal by surveying all of the houses or businesses in the area of the signal. Further, past systems do not allow for the easy determination of the precise location of the ingress source within a house or business.
Because all residences and business locations have the potential to cause problems in the upstream path, a test is needed to qualify each individual residence.